Test WCF service Method from console app, Method not allowed?

Question

I created a WCF service that has a basic method to add two numbers as follows:

[ServiceContract]
public interface IColorService
{
    [OperationContract]
    [WebGet(
        RequestFormat = WebMessageFormat.Json,
        ResponseFormat = WebMessageFormat.Json,
        UriTemplate = "/AddNumber?number1={number1}&number2={number2}")]
    int AddNumber(string number1, string number2);

}
public class ColorService : IColorService
{
    public int AddNumber(string number1, string number2)
    {
        int num1 = Convert.ToInt32(number1);
        int num2 = Convert.ToInt32(number2);
        return num1 + num2;
    }

I host the service on IIS 7.5. I check that it is running and getting back the correct result from the IE, as I typed "http://localhost/ColorsService/ColorService.svc/AddNumber?nubmer1=100&number2=200" and I got the result.

I created a Console application to test the WCF service and put the correct configuration in the app.config & also I added the service reference.

Here is the code I have to call the service

Service.ColorServiceClient client = new Service.ColorServiceClient();

double v = client.AddNumber("12", "15");
Console.WriteLine();

When I run the application I got this error : (405) Method Not Allowed !!

Can anyone help